The metal panel on the left wall is a basic box shape that is repeated but I didn't want to map the whole section. So in order to get grime in the correct areas I unwrapped one complete section and then duplicated this piece of geometry which then carried the UV co-ordinates through. In Fig.04 you can see the texture for the entire panel which corresponds to one section of the geometry. In order to avoid any obvious and repeatable patterns I manually tweaked some of the UV's on each panel section so that they were not identical - the bane of tiling textures!

I followed the same procedure for the ceiling supports.

Fig. 04

The floor area is perhaps the largest unbroken section of the scene and so required a map that would tile so as to reduce the texture size. However the drawback of not unwrapping geometry comes when wanting to localise dirt in specific areas. The way to counter this is by using a Blend map (Fig.05).

Fig. 05

Here we can see the Blend map consisting of two materials and a mask. Material 1 is the clean floor and most of what is seen in the render. Material 2 represents the dirty floor. Both textures are tiled by the same amount but in the Mask channel we have a greyscale map. This is not tiled and because it is greyscale it is a smaller file size and hence can be far bigger in scale (Fig.06). Here you can see the mask map where pure white denotes opacity (dirty floor) and black represents the transparent areas (clean floor). You can see that the dirt has been restricted to the edges of objects such as the column and steps.

When applied, the white areas of the mask enable the darker texture (material 2) to show through the clean texture (Material 1).